Method of manufacturing image sensor unit

ABSTRACT

There is provided a method of manufacturing an image sensor unit, the image sensor unit including: a linear light source that illuminates a document along a main scanning direction; a rod lens array that includes a plurality of rod lenses arranged in the main scanning direction and condenses a light reflected from the document; and a linear image sensor that receives a light condensed by the rod lens array. When a rod lens having an optically discontinuous portion on a surface and/or interior of the rod lens is included, the rod lens array is arranged such that the optically discontinuous portion is not located toward the document.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method of manufacturing an imagesensor unit primarily used in an image reading device.

2. Description of the Related Art

In the related art, some image reading devices such as scanners areknown to use an erecting equal-magnification optical system. The use ofan erecting equal-magnification optical system can reduce the size ofthe image sensor unit better than reduction optical systems. An imagesensor unit using an erecting equal-magnification optical systemprimarily comprises a linear light source, an erectingequal-magnification lens array, a linear image sensor, and a housingthat fixes these components at predetermined positions.

An image sensor unit using an erecting equal-magnification opticalsystem is designed such that the best optical performance is exhibitedwhen the distance between the document and the erectingequal-magnification lens array is identical to the distance between theerecting equal-magnification lens array and the linear image sensor. Ifthe distances are not identical, the optical performance will be poordue to blurred images. Therefore, in consideration of the fact that adocument is planar, the erecting equal-magnification lens array and thelinear image sensor are built in the housing in a linear fashion suchthat they are parallel to the document.

An erecting equal-magnification optical system is exemplified by aSELFOC Lens Array (SLA, SELFOC is a registered trademark of Nippon SheetGlass Co. Ltd.), which is a form of rod lens array including a largenumber of rod lenses arranged in the main scanning direction andintegrated with each other, each of the rod lens including a columnargraded index glass rod having a higher refraction index at the center.Other known examples include a resin rod lens array including a largenumber of graded index resin rod lenses arranged in the main scanningdirection and integrated with each other, and a lens array plate or astack thereof produced by forming a large number of convex lenses on thesurface of a dielectric substrate plate.

Among the various types, SLA is extensively used in the aforementionedapplications. SLA is not only highly durable due to the glass materialbut the optical performance thereof is extremely high as compared toother optical systems (see, for example, patent document 1). Resin rodlens arrays are also used extensively because of their low prices.

[Patent Document 1] JPH11-64605

Optical systems used in scanners and image reading applications arerequired to exhibit extremely high imaging performance and contrastperformance. Therefore, depending on the required performance andquality, a high standard is also required in regard to the defects andflaws on the surface and interior of the lens. In optical systemscontaining an optically discontinuous portion, etc. due to dents andlosses of a groove shape such as chips, fractures, cracks, andscratches, a phenomenon outside the design such as a flare occurs due tounintended scattering, reflection, refraction, etc. at the interface orin the interior of the optically discontinuous portion, which couldpossibly result in a significant drop in the optical performance. Hence,a high standard for performance is required. It is also known that if animage sensor unit in which such an optical system is mounted is used tomanufacture an image reading device, the optical performance isadversely affected. For example, white streaks appear in read images, orthe contrast is degraded due to an impact from a flare.

SUMMARY OF THE INVENTION

The present invention addresses the issue and a purpose thereof is toprovide a method of manufacturing an image sensor unit capable ofpreventing the optical performance from being degraded even if anerecting equal-magnification lens array including an opticallydiscontinuous portion on the surface or interior of the lens is used inthe image sensor unit.

The method of manufacturing an image sensor unit according to at leastone embodiment of the present invention is adapted for an image sensorunit comprising: a linear light source that illuminates a documentplaced on an original platen glass along a main scanning direction; anerecting equal-magnification lens array that includes a plurality ofsingle lenses arranged in the main scanning direction and condenses alight reflected from the document; and a linear image sensor thatreceives a light condensed by the erecting equal-magnification lensarray. When the single lenses constituting the erectingequal-magnification lens array include a single lens having an opticallydiscontinuous portion on at least one of an incident face, a emissionface and an interior of the single lens, the erecting equalmagnification lens array is arranged such that an interface of theoptically discontinuous portion, extending from an end face of thesingle lens facing the document toward the linear image sensor and in adirection away from a direction in which illuminating light from thelinear light source is incident on the original platen glass, is notlocated toward the document.

The main scanning direction of the linear light source is thelongitudinal direction of the linear light source. The linear lightsource substantially evenly irradiates a document with light(illuminating light) linearly along the longitudinal direction. The mainscanning direction of the erecting equal-magnification lens array is thelongitudinal direction of the erecting equal-magnification lens array.The erecting equal-magnification lens array condenses a light reflectedfrom the document irradiated by the linear light source to create anerecting equal-magnification image on the linear image sensor.

According to the embodiment, the optical performance is prevented frombeing degraded due to any optically discontinuous portion located in/onthe erecting equal-magnification lens array. It is therefore possible toprovide an image sensor unit that allows, when used in an imageprocessing device, obtaining read images of favorable quality.

In further accordance with the embodiment, an image sensor unit and animage reading device can be manufactured without degrading the opticalperformance even if the erecting equal-magnification lens array includesa quality defect such as a crack, chip, scratch, etc. that forms anoptically discontinuous portion. Erecting equal-magnification lensarrays and image sensor units that were hitherto disposed of as rejectedproducts due to the defect can be regenerated or saved so that thesubstantial fabrication yield is improved and the manufacturing cost isreduced.

The linear light source may be adjacent to the erectingequal-magnification lens array, and an irradiation surface of the linearlight source is arranged to face an intersection between an optical axisof the erecting equal-magnification lens array and a top surface of theoriginal platen glass.

When the single lenses constituting the erecting equal-magnificationlens array include a single lens having an optically discontinuousportion on at least one of an incident face, a emission face and aninterior of the single lens, the erecting equal magnification lens arraymay be arranged such that the optically discontinuous portion is locatedtoward the linear image sensor.

An optically discontinuous portion, if present in a light path, causeslight rays to undergo unintended scattering, refraction, reflection,attenuation, etc. An optically discontinuous portion may accompany anirregularity or a loss and adversely affects the optical performance.The optically discontinuous portion may be at least one of a chip,fracture, crack, cleavage, striae, pit, and scratch. In manymanufacturing scenes, erecting equal-magnification lens arrays thatinclude an optically discontinuous portion as described above aresystematically removed in an inspection step according to a givenstandard. A lens surface also represents a discontinuous interfacebetween a lens medium and air, etc. However, a lens surface does notinitiate unintended refraction, reflection, etc. and produces opticalperformance expected in the design by providing refraction at theinterface. Therefore, a lens surface is not designated as an opticallydiscontinuous portion in this specification.

The erecting equal-magnification lens array may be a rod lens arrayincluding a plurality of rod lenses. The plurality of rod lenses may bearranged in a single line in the main scanning direction.

A direction angle of the interface of the optically discontinuousportion may be less than 20°. As described later, a direction angle ofthe interface of an optically discontinuous portion of less than 20° islikely to degrade the optical performance. The optical performance isprevented from being degraded by arranging the interface of an opticallydiscontinuous portion having a direction angle of less than 20° so asnot to be located toward the document.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses,etc. may also be practiced as additional modes of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 shows an image reading device in which an image sensor unitaccording to the embodiment of the present invention is used;

FIGS. 2A and 2B are schematic views of a rod lens including an opticallydiscontinuous portion in the form of a chip;

FIGS. 3A and 3B are schematic view of a rod lens including an opticallydiscontinuous portion in the form of a scratch;

FIG. 4 is a schematic view of a rod lens array used in a simulation;

FIG. 5 is a schematic sectional view showing the image sensor andexamples of light paths of light rays used in the simulation;

FIG. 6 is a schematic sectional view showing the position and directionof the interface of an optically discontinuous portion included in a rodlens used in the simulation;

FIG. 7 is a schematic plan view of the rod lens used in the simulationviewed from the document side, showing the positions and directions ofinterfaces belonging to (i) and (ii);

FIG. 8 is a schematic plan view of the rod lens used in the simulationviewed from the linear image sensor side, showing the positions anddirections of interfaces belonging to (iii) and (iv);

FIG. 9 is a graph showing how the light intensity ratio varies as thedirection angle θ of the interface varies;

FIGS. 10A-10C show a rod lens used as a model to perform the simulationof FIG. 9;

FIG. 11 is a graph showing how the light intensity ratio varies as theposition X of the interface varies;

FIGS. 12A-12C show a rod lens used as a model to perform the simulationof FIG. 11;

FIG. 13 is a graph showing how the light intensity ratio varies as thedepth d of the interface varies;

FIGS. 14A-14C show a rod lens used as a model to perform the simulationof FIG. 13;

FIG. 15 is a graph showing how the light intensity ratio varies as thewidth w of the interface varies;

FIGS. 16A-16C show a rod lens used as a model to perform the simulationof FIG. 15;

FIG. 17 is a schematic sectional view showing light paths of light raysin a rod lens array including an interface of an optically discontinuousportion belonging to (ii) shown in FIG. 6;

FIG. 18 is a schematic sectional view showing light paths of light raysin a rod lens array including an interface of an optically discontinuousportion belonging to (iii) shown in FIG. 6;

FIG. 19 is a schematic sectional view showing light paths of light raysin a rod lens array including an interface of an optically discontinuousportion belonging to (iv) shown in FIG. 6;

FIG. 20 shows an embodiment in which a chip is located at a certainposition in a rod lens;

FIG. 21 is a schematic sectional view showing an embodiment in which achip is at a certain position in a rod lens;

FIG. 22 shows another embodiment in which a chip is located at a certainposition in a rod lens;

FIG. 23 is a schematic sectional view showing another embodiment inwhich a chip is at a certain position in a rod lens;

FIG. 24 shows an embodiment in which a scratch is located at a certainposition in a rod lens;

FIG. 25 is a schematic sectional view showing an embodiment in which ascratch is at a certain position in a rod lens;

FIG. 26 shows another embodiment in which a scratch is located at acertain position in a rod lens; and

FIG. 27 is a schematic sectional view showing another embodiment inwhich a scratch is at a certain position in a rod lens.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

FIG. 1 shows an image reading device 100 in which an image sensor unit10 according to the embodiment of the present invention is used. Theimage sensor unit 10 is elongated in a direction perpendicular to thepaper surface and FIG. 1 shows a cross section of the image sensor unit10 revealed by cutting the image sensor unit 10 by a plane parallel tothe surface of the paper. As shown in FIG. 1, the image reading device100 comprises an image sensor unit 10, an original platen glass 13configured to support a document G on a top surface 131, a drivingmechanism (not shown) for driving the image sensor unit 10, and an imageprocessing unit (not shown) for processing data read by the image sensorunit 10.

The image sensor unit 10 comprises a linear light source 14 forilluminating a document G placed on the original platen glass 13, anerecting equal-magnification lens array 11 for condensing a lightreflected from the document G, a linear image sensor (photoelectrictransducer) 15 for receiving light condensed by the erectingequal-magnification lens array 11, and a housing 12 that fixes thesecomponents.

Referring to FIG. 1, the direction of the arrow (direction parallel tothe surface of the paper) represents the sub-scanning direction and thedirection perpendicular to the sub-scanning direction is the mainscanning direction. The erecting equal-magnification lens array 11 iselongated in the main scanning direction and a plurality of lenses arearranged in a single line or in two or more lines along the mainscanning direction and are integrated with each other. The linear lightsource 14 is also elongated in the main scanning direction andilluminates the document linearly along the main scanning direction. Thelinear image sensor 15 includes a plurality of photoelectric transducersarranged on a substrate elongated in the main scanning direction andalong the main scanning direction. The housing 12 is substantiallyrectangular in shape and elongated in the main scanning direction.

The housing 12 has the function of fixing the erectingequal-magnification lens array 11, the linear light source 14, and thelinear image sensor 15 so as to maintain predetermined relativepositions. These components elongated in the main scanning direction arearranged substantially parallel to the main scanning direction. Theoptical axis Ax of the erecting equal-magnification lens array 11 isarranged to be perpendicular to the principal surface of the originalplaten glass 13. Further, the linear light source is arranged such thatthe illumination light illuminates an area F including an intersection fbetween the optical axis Ax of the erecting equal-magnification lensarray 11 and the top surface 131 evenly and most brightly. The linearimage sensor 15 is fixed in the housing 12 such that it is located onthe optical axis Ax and an erecting equal-magnification image of theintersection f is formed on the light receiving surface via the erectingequal-magnification lens array 11. The image sensor unit 10 is mountedto the image reading device 100 such that the image sensor unit 10 isdriven in the sub-scanning direction.

In the image reading device 100, the illuminating light from the linearlight source 14 irradiates the document G via the original platen glass13. The image reading device 100 is capable of reading the document G bycausing the erecting equal-magnification lens array 11 to condense alight reflected from the document G and forming an image of the light onthe linear image sensor 15, and, is further capable of reading a desiredarea on the document G by causing the image sensor unit 10 to scan thedocument G in the sub-scanning direction relative to the original platenglass 13.

Described above is a schematic configuration of the image sensor unit 10and the image reading device 100. A description will be given of afeature of the present invention.

In the image sensor unit 10 according to the embodiment, the surfaceand/or the interior of the lenses in the erecting equal-magnificationlens array may include a chip, fracture, crack, cleavage, ripple mark,striae, pit, scratch, etc. which result in optically discontinuousportions. Such portions in an optical system may produce light due toscattering, refraction, or reflection outside the design. A chip, whichis an example of optically discontinuous portion, is a generic term thatgenerally refers to a pinhole and clamshell chip. A fractured portioninside the lens that is not dislocated from the lens surface butpotentially creates a chip will also be referred to as a chip. Anoptically discontinuous portion is not limited to those referred to bythe specific terms illustratively used above. The term refers to aportion that produces scattering, refraction, or reflection outside thedesign, or a portion that consequently creates a cause such as flare orghost resulting in degradation of optical performance.

The manufacturing process of an erecting equal-magnification lens arraysuch as an SLA made of glass may include cutting, grinding, polishing,etc. Due to the brittleness and characteristics inherent in themanufacturing steps of the glass material, an optically discontinuousportion such as a chip, fracture, crack, scratch, etc. may be createdinside and outside the lens. A striae inside the lens is not directlyrelevant to the characteristics inherent in the manufacturing steps butis created due to unevenness in phase or composition when a glass havinga certain composition is formed by a melting method or the like and isknown to be a cause to induce unintended refraction of light, etc.outside the design.

The manufacturing process of a rod lens array including resin rod lensesarranged in the main scanning direction also includes, in many cases, acutting step or a polishing step so that the same situation as that ofthe erecting equal-magnification lens array made of glass holds asregards an optically discontinuous portion, except that, due to thesoftness of the material, a scratch presents a problem more often thanthat in the case of glass rod lenses.

Meanwhile, a lens array plate produced by forming a plurality of convexlenses on at least one principal surface of a transparent dielectricsubstrate is primarily formed by a press process using a mold forinjection molding, etc. The press molding seldom involves steps likepolishing described above directly. However, an optically discontinuousportion exemplified above by a chip, fracture, crack, scratch, etc. maybe created due to the condition of the mold or the condition ofpressing. A sink may also be created inside and/or outside the lensdepending on the condition during pressing. A sink is also known as acause to induce unintended optical light refraction and so can bedefined as an optically discontinuous portion.

Two examples of optically discontinuous portions of a rod lens will bediscussed.

FIGS. 2A and 2B show a chip 32 created in a rod lens 30. FIG. 2A showsan end face of the rod lens 30, and FIG. 2B shows a cross section of therod lens 30 revealed by cutting the rod lens 30 by a plane passingthrough the optical axis and parallel to the optical axis. As shown inFIGS. 2A and 2B, the chip 32 includes an interface 201 between the lensmedium and air.

FIGS. 3A and 3B show a scratch 33 created in the rod lens 30. FIG. 3Ashows an end face of the rod lens 30, and FIG. 3B shows a cross sectionof the rod lens 30 revealed by cutting the rod lens 30 by a planepassing through the optical axis and parallel to the optical axis. Asshown in FIGS. 3A and 3B, the scratch 33 includes interfaces 202 and 203between the lens medium and air.

The figures show that the two examples of optically discontinuousportions (i.e., the chip 32 and the scratch 33) include an interfacethat induces light refraction, reflection, etc. It should be noted thatother optically discontinuous portions having a similar behavior arealso targeted by the present invention.

A simulation was conducted to see how the optical performance isaffected when an erecting equal-magnification lens array including alens with an optically discontinuous portion is built into the erectingequal-magnification lens array. By way of example of the erectingequal-magnification lens array 11, a rod lens array including an arrayof graded index rod glass lenses (SLA12E rod lens array from NipponSheet Glass Co. Ltd. (an individual lens has a lens aperture angle of12°, effective diameter of 0.28 mm, pitch of lens arrangement of 0.3mm)) arranged in a single line, the number of lenses included in thearray being 21, is used. FIG. 4 is a schematic view of a rod lens array31 described above. The side surfaces of the glass rod lens 30 formedwith a graded index inside are cladded for light absorption and/orcoated black for light absorption (not shown). The cladding or coatingrapidly attenuates light rays deviated from the light path as designedas they reach the neighborhood of the side surfaces and inhibitspropagation inside the lens and emission from the lens, therebypreventing occurrence of a flare etc. that does not contribute toimaging. The rod lenses 30 are sandwiched by two side plates 301 made ofan elongated, light absorbing fiber-reinforced plastic (FRP). Inconducting a simulation, the rod lens array 31, the linear light source14, the original platen glass 13, and the linear image sensor 15 arearranged according to the specification of the image sensor unit 10 asdescribed with reference to FIG. 1.

FIG. 5 is a diagram showing the arrangement of the components and pseudolight rays used in the simulation. The housing is irrelevant for thepurpose of simulation and is omitted from the illustration in FIG. 5. Inthe simulation, regressivity of light is considered. Pseudo light raysare emitted from the linear image sensor 15 to travel a light pathopposite to the light path expected in the actual image sensor unit, andthe behavior of the light rays after impinging upon the opticallydiscontinuous portion of the lens is determined by computation based onray tracing. For pseudo light emission, a 5 micrometer by 5 micrometersquare pixel of the linear image sensor is assumed as a pseudo lightemission point and a model is conceived in which 10000 light rays withan even intensity having a wavelength of 530 nm are emitted atLambertian 12°.

An optically discontinuous portion having an air layer of about 1micrometer at the interface defined by the optically discontinuousportion is assumed. The lens is assumed to include the opticallydiscontinuous portion with such an interface. For the purpose ofidentifying the location of the optically discontinuous portion in thelens, the thickness of the rod lens is sectioned right in the middle bya plane perpendicular to the optical axis of the lens as shown in FIG.5. The optically discontinuous portion is identified as being locatedeither in the portion (of the lens) “toward the document” (portiondenoted by numeral 111) or the portion (of the lens) “toward the linearimage sensor” (portion denoted by numeral 112). The direction away fromthe document and toward the linear image sensor will be defined as“downward” and the opposite direction as “upward”.

In the simulation, one rod lens including an optically discontinuousportion with a certain interface is provided right in the middle of thearray of the rod lens array 31 described above. The 5 micrometer by 5micrometer square pixel of the linear image sensor located immediatelybeneath the optical axis of the rod lens 30 including the opticallydiscontinuous portion is caused to emit pseudo light. In the absence ofthe lens including the optically discontinuous portion, or in the caseof light rays not affected by optically discontinuous portions, thelight rays are condensed in a region (referred to as light condensationregion F) near an intersection f between the optical axis Ax of the lensand the top surface 131 of the original platen glass 13 as indicated bya light ray 41 denoted by the broken line. Meanwhile, if a rod lenshaving an optically discontinuous portion in its interior or on itssurface is included, an interface 411 included in the opticallydiscontinuous portion induces reflecting or refracting light outside thedesign. Some light rays are emitted from the rod lens 30, reflected bythe top surface 131 or a bottom surface 132 of the original platen glass13, before reaching an irradiation surface 141 of the linear lightsource 14, as indicated by light rays 42 and 43 denoted by the two-dotchain lines.

For measurement of the impact from the optically discontinuous portion,the intensity I₁ of a portion of the light rays from pseudo lightemission refracted or reflected by the interface 411 of the opticallydiscontinuous portion and reaching the irradiation surface 141 of thelinear light source 14 as indicated by the light ray 42 or 43 iscalculated, the intensity I₀ of light rays from light emission travelingon a light path as designed without being affected by the interface 411and reaching the light condensation region F on the document G asindicated by the light ray 41 is calculated, and the ratio I₁/I₀ of theformer light intensity to the latter light intensity (light intensityratio in the presence of the optically discontinuous portion;hereinafter, referred to as light intensity ratio) is calculated. Itshould be noted that the light rays 41, 42, and 43 shown in FIG. 5 areexamples of light rays reaching a target region and, in reality, a largenumber of light beams reach the respective target regions via similarlight paths.

In light of the principle of regressivity of light, the above resultshowing that the pseudo light ray emitted from the linear image sensor15 reaches the irradiation surface 141 of the linear light source 14under the impact from the optically discontinuous portion in thesimulation, is mirrored in an optical system including an actual imagesensor by a portion of the illumination light emitted from theirradiation surface 141 of the linear light source 14 being reflected orrefracted contrary to the design by the optically discontinuous portionincluded in the rod lens 30 and reaching the linear image sensor 15.

The light does not contribute to imaging of the document G on the linearimage sensor 15, which is the action of the optical system as designed,but is considered to provide an impact such as reduced contrast due to aflare or white streaks in the resultant image.

The interface included in the optically discontinuous portion in the rodlens is assumed to be located at positions and in orientations as shownin (i)˜(iv) of FIG. 6. FIG. 6 is a side view revealed by cutting the rodlens 30 that includes an interface of an optically discontinuous portionby a plane including the interface and parallel to the optical axis,when it is assumed that the rod lens 30 is oriented such that thedirection indicated by an arrow A in the figure is toward the linearlight source, the direction indicated by an arrow B in the figure istoward the document, and the direction indicated by an arrow C in thefigure is toward the linear image sensor. FIG. 7 is a plan view of theend face of the rod lens as viewed from the side of the document, andFIG. 8 is a plan view of the end face of the rod lens as viewed from theside of the linear image sensor. The position and direction of (i)indicate that the optically discontinuous portion having that interfaceis located toward the document and the direction of the interfaceextending from the end face of the rod lens 30 facing the document isdownward and is oriented away from the linear light source. The positionand direction of (ii) indicate that the optically discontinuous portionhaving that interface is located toward the document and the directionof the interface extending from the end face of the rod lens 30 facingthe document is downward and is oriented toward the linear light source.The position and direction of (iii) indicate that the opticallydiscontinuous portion having that interface is located toward the linearimage sensor and the direction of the interface extending from the endface of the rod lens 30 facing the linear image sensor is upward and isoriented away from the linear light source. The position and directionof (iv) indicate that the optically discontinuous portion having thatinterface is located toward the linear image sensor and the direction ofthe interface extending from the end face of the rod lens 30 facing thelinear image sensor is upward and is oriented toward the linear lightsource. The interfaces described above are planar. As shown in FIG. 7,the interfaces belonging to (i) and (ii) or lines of intersectionbetween planes extending from the interfaces and the end face of the rodlens facing the document are perpendicular to the direction indicated bythe arrow A in the figure. As shown in FIG. 8, the interfaces belongingto (iii) and (iv) or lines of intersection between planes extending fromthe interfaces and the end face of the rod lens facing the linear imagesensor are perpendicular to the direction indicated by the arrow A inthe figure. For example, the interface of the optically discontinuousportion shown in FIG. 5 has the attribute of (i).

FIG. 9 is a graph calculated based on a simulation to see how the lightintensity ratio varies as the direction angle of the planar interfacedefined by the position and direction of (i) is changed. The directionangle is an angle formed by the interface and the optical axis. FIGS.10A-10C show an interface of an optically discontinuous portion used inthe simulation. FIG. 10A shows an end face of the rod lens 30, FIG. 10Bshows a cross section of the rod lens 30, and FIG. 10C shows a side faceof the rod lens 30. The rod lens array 31 is installed in theconfiguration shown in FIG. 5 to orient the rod lens 30 including anoptically discontinuous portion having an interface 62 as shown in FIGS.10A-10C such that the direction indicated by the arrow A in the figureis toward the linear light source, the direction indicated by the arrowB in the figure is toward the document, and the direction indicated bythe arrow C is toward the linear image sensor.

As shown in FIG. 10A, a line of intersection 63 between the interface 62and an end face 61 facing the document is perpendicular to the directionindicated by the arrow A in the figure indicating a direction toward thelinear light source. Denoting the effective diameter of the rod lens 30by D, the line of intersection 63 is located at a distance of D/4 fromthe center of the rod lens 30. The width w₁ of the line of intersection63 is a length extending from end to end of the effective region of theend face 61 of the rod lens 30 facing the document and is such thatw₁=0.242 mm. The interface 62 extends from the line of intersection 63through the interior and reaches the side surface of the rod lens 30.

The horizontal axis of FIG. 9 represents the direction angle θ(°) of theinterface 62, and the vertical axis represents the light intensity ratioI₁/I₀ (%). The solid line indicates the light intensity ratio I₁/I₀,where I₁ is defined as a sum of the intensity of a light reflected bythe top surface 131 of the original platen glass 13 and reaching theirradiation surface 141 of the linear light source 14 and the intensityof a light reflected by the bottom surface 132 of the original platenglass 13 and reaching the irradiation surface 141 of the linear lightsource 14. The broken line indicates the light intensity ratio I₁/I₀,where I₁ is defined as the intensity of a light reflected by the bottomsurface 132 of the original platen glass 13 and reaching the irradiationsurface 141 of the linear light source 14.

As shown in FIG. 9, the light intensity ratio reaches 0 when thedirection angle of the interface 62 is 20° or greater. This means thatsome light rays are reflected by the interface but are not emittedoutside the rod lens 30 or, even if they are emitted, do not reach theirradiation surface 141 of the linear light source 14.

Since the light intensity ratio determined by totaling the reflectionfrom the top surface and the bottom surface is required to be 0.5% orlower, and, preferably, 0.1% or lower, FIG. 9 reveals that the directionangle of the interface of less than 20° presents a problem.

FIG. 11 is a graph calculated based on a simulation to see how the lightintensity ratio varies as the position of the planar interface definedby the position and direction of (i) in the diametrical direction of therod lens 30 is changed. FIGS. 12A-12C show an interface 72 of anoptically discontinuous portion used in the simulation. FIG. 12A showsan end face of the rod lens 30, FIG. 12B shows a cross section of therod lens 30, and FIG. 12C shows a side face of the rod lens 30. The rodlens array 31 is installed in the configuration shown in FIG. 5 toorient the rod lens 30 including an optically discontinuous portionhaving the interface 72 as shown in FIGS. 12A-12C such that thedirection indicated by the arrow A in the figure is toward the linearlight source, the direction indicated by the arrow B in the figure istoward the document, and the direction indicated by the arrow C istoward the linear image sensor.

As shown in FIGS. 12A-12C, a line of intersection 73 between theinterface 72 and an end face 71 facing the document is perpendicular tothe direction indicated by the arrow A in the figure indicating adirection toward the linear light source. The width w₂ of the line ofintersection 73 is a length extending from end to end of the effectiveregion of the end face 71 of the rod lens 30 facing the document. Thedepth d₁ of the interface 72 from the end face 71 facing the document isassumed to be 0.1 mm and the direction angle θ₁ is assumed to be 15°.The position X indicates a distance from a point 0 on the end face 71facing the document farthest from the linear light source.

The horizontal axis of FIG. 11 represents the position X (mm) of theinterface on the lens end face with reference to the effective diameterD of the rod lens 30. The vertical axis represents the light intensityratio I₁/I₀ (%). The solid line indicates the light intensity ratioI₁/I₀, where I₁ is defined as a sum of the intensity of a lightreflected by the top surface 131 of the original platen glass 13 andreaching the irradiation surface 141 of the linear light source 14 andthe intensity of a light reflected by the bottom surface 132 of theoriginal platen glass 13 and reaching the irradiation surface 141 of thelinear light source 14. The broken line indicates the light intensityratio I₁/I₀, where I₁ is defined as the intensity of a light reflectedby the bottom surface 132 of the original platen glass 13 and reachingthe irradiation surface 141 of the linear light source 14.

Since the light intensity ratio determined by totaling the reflectionfrom the top surface and the bottom surface is required to be 0.5% orlower, and, preferably, 0.1% or lower, FIG. 11 reveals that the positionof the interface in the range of 0.35 D˜0.75 D particularly presents aproblem.

FIG. 13 is a graph calculated based on a simulation to see how the lightintensity ratio varies as the depth d of the planar interface defined bythe position and direction of (i) from the end face of the rod lens 30facing the document is changed. FIGS. 14A-14C show an interface 82 of anoptically discontinuous portion used in the simulation. FIG. 14A showsan end face of the rod lens 30, FIG. 14B shows a cross section of therod lens 30, and FIG. 14C shows a side face of the rod lens 30. The rodlens array 31 is installed in the configuration shown in FIG. 5 toorient the rod lens 30 including an optically discontinuous portionhaving the interface 82 as shown in FIGS. 14A-14C such that thedirection indicated by the arrow A in the figure is toward the linearlight source, the direction indicated by the arrow B in the figure istoward the document, and the direction indicated by the arrow C istoward the linear image sensor.

As shown in FIGS. 14A-14C, a line of intersection 83 between theinterface 82 and an end face 81 facing the document is perpendicular tothe direction indicated by the arrow A in the figure indicating adirection toward the linear light source. Since the line of intersection83 passes through the center of the rod lens 30, the width w₃ of theline of intersection 83 is equal to the effective diameter D of the rodlens 30 and is such that w₃=0.28 mm. The direction angle θ₂ of theinterface 82 is assumed to be 18°.

The horizontal axis of FIG. 13 represents the depth d (mm) of theinterface, and the vertical axis represents the light intensity ratioI₁/I₀ (%). The solid line indicates the light intensity ratio I₁/I₀,where I₁ is defined as a sum of the intensity of a light reflected bythe top surface 131 of the original platen glass 13 and reaching theirradiation surface 141 of the linear light source 14 and the intensityof a light reflected by the bottom surface 132 of the original platenglass 13 and reaching the irradiation surface 141 of the linear lightsource 14. The broken line indicates the light intensity ratio I₁/I₀,where I₁ is defined as the intensity of a light reflected by the bottomsurface 132 of the original platen glass 13 and reaching the irradiationsurface 141 of the linear light source 14.

Since the light intensity ratio determined by totaling the reflectionfrom the top surface and the bottom surface is required to be 0.5% orlower, and, preferably, 0.1% or lower, FIG. 13 reveals that the depth ofthe interface of 0.01 mm or greater, and, in particular, 0.03 mm orgreater, presents a problem.

FIG. 15 is a graph calculated based on a simulation to see how the lightintensity ratio varies as the width w of the line of intersectionbetween the planar interface defined by the position and direction of(i) and the end face of the rod lens facing the document is changed.FIGS. 16A-16C show an interface of an optically discontinuous portionused in the simulation. FIG. 16A shows an end face of the rod lens 30,FIG. 16B shows a cross section of the rod lens 30, and FIG. 16C shows aside face of the rod lens 30. The rod lens array 31 is installed in theconfiguration shown in FIG. 5 to orient the rod lens 30 including anoptically discontinuous portion having the interface 92 as shown inFIGS. 16A-16C such that the direction indicated by the arrow A in thefigure is toward the linear light source, the direction indicated by thearrow B in the figure is toward the document, and the directionindicated by the arrow C is toward the linear image sensor.

As shown in FIGS. 16A-16C, a line of intersection 93 between theinterface 92 and an end face 91 facing the document is perpendicular tothe direction indicated by the arrow A in the figure indicating adirection toward the linear light source, and the center of the rod lensbisects the line of intersection 93. The depth d₃ of the interface 92from the end face 91 toward the document is assumed to be 0.2 mm and thedirection angle θ₃ is assumed to be 18°.

The horizontal axis of FIG. 15 represents the width w (mm) of theinterface 92, and the vertical axis represents the light intensity ratioI₁/I₀ (%). The solid line indicates the light intensity ratio I₁/I₀,where I₁ is defined as a sum of the intensity of a light reflected bythe top surface 131 of the original platen glass 13 and reaching theirradiation surface 141 of the linear light source 14 and the intensityof a light reflected by the bottom surface 132 of the original platenglass 13 and reaching the irradiation surface 141 of the linear lightsource 14. The broken line indicates the light intensity ratio I₁/I₀,where I₁ is defined as the intensity of a light reflected by the bottomsurface 132 of the original platen glass 13 and reaching the irradiationsurface 141 of the linear light source 14.

Since the light intensity ratio determined by totaling the reflectionfrom the top surface and the bottom surface is required to be 0.5% orlower, and, preferably, 0.1% or lower, FIG. 15 reveals that the width ofthe interface of 0.01 mm or greater, and, in particular, 0.04 mm orgreater, presents a problem.

Meanwhile, simulations were conducted in consideration of a modelsimilar to the one described above, in which the interface is located inthe position and direction of (ii)˜(iv) in FIG. 6, and the directionangle of the interface, the position of the interface, the depth of theinterface, and the width of the interface are varied. Light rays passingthrough a light path outside the design due to reflection or refractionat the interface are found but none are identified as reaching theirradiation surface 141 of the linear light source 14.

FIG. 17 shows how light rays are reflected or refracted by an interface511 having the attribute of (ii) in FIG. 6. Referring to FIG. 17, areflecting light 513 from the interface 511 is emitted from the rod lens30 but travels in a direction opposite to the direction toward thelinear light source. Therefore, there are hardly any light rays thatreach the irradiation surface 141. The air layer at the interfaceassumed to be located in the optically discontinuous portion isextremely thin. Therefore, refraction at the interface 511 hardlyaffects the light path and no light rays are produced that travel towardthe irradiation surface 141 of the linear light source 14.

FIG. 18 shows how light rays are reflected or refracted by an interface611 having the attribute of (iii) in FIG. 6. Referring to FIG. 18, areflecting light 613 from the interface 611 travels toward the sidesurface of the rod lens 30. As described above, the side surfaces of therod lens 30 are cladded or coated for light absorption and are designednot to propagate light rays deviated from the light path as designed.Therefore, the reflecting light 613 is rapidly attenuated so that thereare hardly any light rays emitted from the rod lens 30. Meanwhile,refraction at the interface 611 hardly affects the light path asdescribed above. Therefore, no light rays traveling to the irradiationsurface 141 of the linear light source 14 are produced from the lightrefracted by the interface 611. Further, even if the light path isaffected by refraction, the refracted light is attenuated by beingabsorbed at the side surface of the rod lens before reaching the endface facing the document and is hardly emitted from the rod lens 30.

FIG. 19 shows how light rays are reflected or refracted by an interface711 having the attribute of (iv) in FIG. 6. Referring to FIG. 19, areflecting light 713 from the interface 711 travels toward the sidesurface of the rod lens 30 and so is rapidly attenuated as describedabove in connection with (iii) so that there are hardly any light raysemitted from the rod lens 30. Further, as is true of the situationregarding (iii) discussed above, there are hardly any light rays of thelight refracted at the interface 711 that are emitted from the rod lens30.

Based on the foregoing, the likelihood that the light reflected orrefracted by any interface belonging to the position and direction of(ii)˜(iv) in FIG. 6 and located in the rod lens 30 reaches theirradiation surface 141 of the linear light source 14 is extremelysmall.

The study above indicates that adverse impact on an obtained image suchas a flaw like a flare and white streaks is inhibited by at leastconfiguring the image sensor unit such that an interface having anoptically discontinuous portion is not located in the position anddirection of (1).

A study will now be made to see what kind of optically discontinuousportion has the attribute of position and direction of (i).

For example, a consideration is given of a case in which an image sensorunit is configured such that the rod lens 30 having an opticallydiscontinuous portion in the form of the chip 32 as shown in FIGS. 2Aand 2B is located toward the document 111 as shown in FIGS. 20 and 21.FIG. 20 shows a portion of the lens array of the image sensor unithaving the chip 32 as viewed in a direction from the original platenglass, and an arrow A in the figure indicates the direction toward thelinear light source. A line of intersection between an interface 211 andthe end face of the rod lens 30 facing the document is perpendicular tothe direction indicated by the arrow A in the figure. FIG. 21 shows across section of the image sensor unit revealed by cutting the imagesensor unit by a plane perpendicular to the main scanning direction. Theinterface 211 of the chip 32 belongs to (i) in terms of the location anddirection. It is therefore suggested that the interface 211 may affectthe optical performance adversely.

A consideration is further given of a case in which an image sensor unitis configured such that the rod lens 30 having the chip 32 as shown inFIGS. 2A and 2B is located toward the document 111 as shown in FIGS. 22and 23. FIG. 22 shows a portion of the lens array of the image sensorunit having the chip 32 as viewed in a direction from the originalplaten glass, and an arrow A in the figure indicates the directiontoward the linear light source. By decomposing a line of intersectionbetween an interface 221 and the end face of the rod lens 30 facing thedocument into the direction indicated by the arrow A in the figure and adirection perpendicular thereto, the interface would have a componentperpendicular to the direction indicated by the arrow A in the figure.FIG. 23 shows a cross section of the image sensor unit revealed bycutting the image sensor unit by a plane perpendicular to the mainscanning direction. The perpendicular component of the interface 221 ofthe chip 32 belongs to (i) in terms of the location and direction. It istherefore suggested that the interface 221 may affect the opticalperformance adversely.

A consideration is next given of a case in which an image sensor unit 10is configured such that the rod lens 30 having an opticallydiscontinuous portion in the form of the scratch 33 as shown in FIGS. 3Aand 3B is located toward the document 111 as shown in FIGS. 24 and 25.FIG. 24 shows a portion of the lens array of the image sensor unithaving the scratch 33 as viewed in a direction from the original platenglass, and an arrow A in the figure indicates the direction toward thelinear light source. A line of intersection between an interface 222 andthe end face of the rod lens 30 facing the document is perpendicular tothe direction indicated by the arrow A in the figure. FIG. 25 shows across section of the image sensor revealed by cutting the image sensorunit by a plane perpendicular to the main scanning direction. Theinterface 222 of the scratch 33 belongs to (i) in FIG. 6 in terms of thelocation and direction. It is therefore suggested that the interface 222may affect the optical performance adversely.

Meanwhile, an intersection between an interface 223 and the end face ofthe rod lens 30 facing the document is perpendicular to the directionindicated by the arrow A in the figure but the interface 223 belongs to(ii) in FIG. 6 in terms of the direction and orientation. It istherefore suggested that the likelihood that the interface 223 affectsthe optical performance adversely is small.

A consideration is further given of a case in which an image sensor unit10 is configured such that the rod lens 30 having the scratch 33 asshown in FIGS. 3A and 3B is located toward the document 111 as shown inFIGS. 26 and 27. FIG. 26 shows a portion of the lens array of the imagesensor unit 10 having the scratch 33 as viewed in a direction from theoriginal platen glass, and an arrow A in the figure indicates thedirection toward the linear light source. By decomposing a line ofintersection between an interface 232 and the end face of the rod lens30 facing the document into the direction indicated by the arrow A inthe figure and a direction perpendicular thereto, the interface wouldhave a component perpendicular to the direction indicated by the arrow Ain the figure. FIG. 27 shows a cross section of the image sensor unitrevealed by cutting the image sensor unit by a plane perpendicular tothe main scanning direction. The perpendicular component of theinterface 232 of the scratch 33 belongs to (i) in terms of the locationand direction. It is therefore suggested that the interface 232 mayaffect the optical performance adversely.

Meanwhile, by decomposing a line of intersection between an interface233 and the end face of the rod lens 30 facing the document into thedirection indicated by the arrow A in the figure and a directionperpendicular thereto, the interface 233 would have a componentperpendicular to the direction indicated by the arrow A in the figure.However, the perpendicular component of the interface belongs to (ii) inFIG. 6 in terms of the direction and orientation. It is thereforesuggested that the likelihood that the interface 233 affects the opticalperformance adversely is small.

Accordingly, it is suggested that, where an optically discontinuousportion having one or a plurality of interfaces such as the chip 32 andthe scratch 33 is located near the end face of the rod lens 30 facingthe document, the interface may impact the optical performance, whichmay result in reduced contrast due to a flare or occurrence of whitestreaks in images obtained in the image sensor unit 10 or the imagereading device 100 provided with such a structure, provided that a lineof intersection between the interface (or a plane extending therefrom)and the end face of the rod lens 30 toward the document has a componentperpendicular to the direction toward the linear light source.

However, when an optically discontinuous portion having one or aplurality of interfaces such as the chip 32 and the scratch 33 islocated near the end face of the rod lens 30 facing the document, it isdifficult to arrange the rod lens 30 such that a line of intersectionbetween the interface (or a plane extending therefrom) and the end faceof the rod lens 30 facing the document does not have a componentperpendicular to the direction toward the linear light source.Accordingly, the rod lens 30 having an optically discontinuous portionon the surface and/or interior of the erecting equal-magnification lensarray 11 is included in the image sensor unit 10 manufactured, theerecting equal-magnification lens array 11 is arranged such that theoptically discontinuous portion is not located toward the document. Inessence, the erecting equal-magnification lens array 11 is arranged insuch a case that the optically discontinuous portion is located towardthe linear image sensor 15. This prevents reduced contrast due to aflare or occurrence of white streaks so that the optical performance isprevented from being degraded.

By employing the manufacturing method described above, the image sensorunit 10 or the image reading device 100 can be manufactured withoutdegrading the optical performance even if the erectingequal-magnification lens array 11 includes an optically discontinuousportion in the form of a crack, chip, scratch, etc. Therefore, theerecting equal-magnification lens array 11 and the image sensor unit 10that were hitherto disposed of as rejected products due to the defectcan be regenerated or saved. As a result, the yield is improved and themanufacturing cost is reduced.

Described above is an explanation based on an exemplary embodiment. Theembodiment is intended to be illustrative only and it will be understoodby those skilled in the art that various modifications to constitutingelements and processes could be developed and that such modificationsare also within the scope of the present invention.

The embodiment was described above as using an SLA, a rod lens arrayincluding a plurality of rod lenses with a graded index inside arrangedin the main scanning direction, is used as the erectingequal-magnification lens array. However, the substance of the inventionremains unchanged if a resin rod lens array including an array of alarge number of graded index rod lenses is used as the erectingequal-magnification lens array. The same is true of using a lens arrayplate (or a stack thereof) produced by arranging a large number ofconvex lenses on one or both surfaces of a transparent dielectricsubstrate such as a plastic along the main scanning direction, as anerecting equal-magnification lens array.

The description of the embodiment and the simulation was directed to anerecting equal-magnification lens array including rod lenses arranged ina single line in the main scanning direction, but the erectingequal-magnification lens array including two or more lines of lenses arenot outside the scope of the present invention.

What is claimed is:
 1. A method of manufacturing an image sensor unit,the image sensor unit comprising: a linear light source that illuminatesa document placed on an original platen glass along a main scanningdirection; an erecting equal-magnification lens array that includes aplurality of single lenses arranged in the main scanning direction andcondenses a light reflected from the document; and a linear image sensorthat receives a light condensed by the erecting equal-magnification lensarray, wherein when the single lenses constituting the erectingequal-magnification lens array include a single lens having an opticallydiscontinuous portion on at least one of an incident face, a emissionface and an interior of the single lens, the erecting equalmagnification lens array is arranged such that an interface of theoptically discontinuous portion, extending from an end face of thesingle lens facing the document toward the linear image sensor and in adirection away from a direction in which illuminating light from thelinear light source is incident on the original platen glass, is notlocated toward the document.
 2. The method of manufacturing an imagesensor unit according to claim 1, wherein the linear light source isadjacent to the erecting equal-magnification lens array, and anirradiation surface of the linear light source is arranged to face anintersection between an optical axis of the erecting equal-magnificationlens array and a top surface of the original platen glass.
 3. The methodof manufacturing an image sensor unit according to claim 1, wherein whenthe single lenses constituting the erecting equal-magnification lensarray include a single lens having an optically discontinuous portion onat least one of an incident face, a emission face and an interior of thesingle lens, the erecting equal magnification lens array is arrangedsuch that the optically discontinuous portion is located toward thelinear image sensor.
 4. The method of manufacturing an image sensor unitaccording to claim 1, wherein the optically discontinuous portion is atleast one of a chip, fracture, crack, cleavage, striae, pit, andscratch.
 5. The method of manufacturing an image sensor unit accordingto claim 1, wherein the erecting equal-magnification lens array is a rodlens array including a plurality of rod lenses.
 6. The method ofmanufacturing an image sensor unit according to claim 5, wherein theplurality of rod lenses are arranged in a single line in the mainscanning direction.
 7. The method of manufacturing an image sensor unitaccording to claim 1, wherein a direction angle of the interface of theoptically discontinuous portion is less than 20°.